In recent years, a capacity virtualization technique has been used for a storage system and a server computer for the purpose of increasing the intensity to reduce a cost. As the capacity virtualization technique, there can be mentioned a virtual hard disk that is configured to be used for a virtual computer (VM) for instance. For a virtual hard disk file, there are a virtual hard disk of a fixed type in which a file of a size that is equivalent to a disk size of a virtual hard disk is prepared in creation and a virtual hard disk of a variable type in which a file size is extended in accordance with a volume usage size on a virtual hard disk. The virtual hard disk of a variable type consumes only a capacity that is being used as a practical matter. Consequently an extra capacity is not consumed and a resource can be utilized with no waste. A similar capacity virtualization technique exists for a storage system.
In the case where such a capacity virtualization technique is used, since an actual physical capacity and a logical capacity that is allocated to a server/virtual server (virtual machine) are greatly different from each other, a management has a tendency to be complicated. Moreover, in the case where a physical capacity is depleted, there is a real possibility that a work is stopped by a disk I/O error and a virtual computer that is configured to use a virtual hard disk of a variable type on a volume in which a capacity has been depleted is stopped.
As a technique for simplifying a management of a computer system in which a capacity virtualization technique is used and a management is complicated, a technique that is disclosed in Patent Literature 1 is publicly known. The technique that is disclosed in Patent Literature 1 is a technique for executing an extension of a storage pool and a migration of a virtual server in the case where a value that is called an END-TO-END leverage ratio that is a ratio of a total capacity of one or more server level virtual volumes that are corresponded to a storage level pool to a capacity of the storage level pool exceeds a threshold value.